>> But having a single lowercase character with two different
>> uppercase mappings, one currently standard and enshrined in
>> existing casing rules and implementations, one that might one day
>> become standard and require some kind of overriding
>> implementation, seems to me a bit of a standardisation and
>> software development nightmare.
>
> But U+0069 LATIN SMALL LETTER I already has two different full
> uppercase mappings, one default and the other for Turkish and
> Azeri. With uppercase ß, we will have two such indecomposable
> letters.

I think the reason why this proposal gets more attention than any
thousand new CJK characters is that people don't like situations of
this sort. The prospect of explaining that yes, there is now an
uppercase ß, but no, it's not the uppercase of ß--and then, later on,
possibly deciding that yes, uppercase ß eventually will be used as
the uppercase of ß, in certain circumstances--can hardly be
attractive. Nevertheless, if that is the direction that German
orthography is taking, then software must follow.